Short answer: Real licorice root can raise blood pressure and lower potassium because of a compound called glycyrrhizin. NCCIH says even small amounts have been linked to severe effects in people with high blood pressure or heart or kidney disease. In one trial, licorice raised systolic pressure by 3 to 14 mm Hg within two weeks, and in another, adding it to hydrochlorothiazide lowered potassium more than the diuretic alone.
NCCIH explains that licorice root contains glycyrrhizin (glycyrrhizic acid), which "can cause serious adverse effects, such as irregular heartbeat and cardiac arrest, especially when consumed in large amounts or in the long term." It adds that even small amounts of glycyrrhizin from licorice root products have been linked to severe adverse effects in people who eat a lot of salt, people with hypertension, and people with heart or kidney conditions.
A 2017 toxicology review (Nazari 2017) named high blood pressure and problems from low potassium as the most important side effects of licorice and glycyrrhizin, and listed low potassium, older age and female sex among things that make them worse.
In a study in healthy volunteers in Iceland and Sweden (Sigurjonsdottir 2001), people ate 50 to 200 g of licorice a day for 2 to 4 weeks. Systolic blood pressure rose by 3.1 to 14.4 mm Hg, rising with the dose. The authors noted that even 50 g a day for 2 weeks caused a significant rise and that the full effect showed up within 2 weeks.
That pushes against what blood pressure medicines are meant to do. If readings creep up for no clear reason, licorice tea, candy made with real licorice root, or supplements are worth mentioning to the prescriber.
Thiazide diuretics such as hydrochlorothiazide can lower potassium on their own. A small randomized crossover trial (Hukkanen 2009) gave 10 healthy volunteers 32 g of licorice a day, alone and with 25 mg of hydrochlorothiazide, for 2 weeks each:
| Phase | What happened |
|---|---|
| Licorice alone | No change in potassium, blood pressure or heart rate |
| Licorice plus hydrochlorothiazide | Potassium fell by 0.32 mmol/L on average; 2 of 10 people developed low potassium in the first week and stopped early |
The authors suggested asking about licorice habits when a thiazide is started. The trial was small and short, so it shows the direction of the effect more than its size in everyday use.
NCCIH points out that many "licorice" products sold in the US contain no licorice at all; anise oil, which tastes similar, is often used instead. It says oral licorice products without glycyrrhizin (deglycyrrhizinated licorice, or DGL) might be safe for up to 4 months, and that interactions between licorice and corticosteroids have been reported.
NCCIH advises anyone taking medicine to talk with their provider before using licorice or other herbal products. A broader list of herb interactions is on the herbal supplements and medicines page, and potassium-raising medicines are covered on potassium and spironolactone.
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